Figure shows how the ADC0804 is interfaced to a microcompute

Figure shows how the ADC0804 is interfaced to a microcomputer. It shows three control signals, /CS,/RD,and /WR, that come from the microcomputer to the ADC. These signals are used to start each new A/D conversion and to read (transfer) the ADC data output into the microcomputer over the data bus.

Figure shows one way the address decoding logic could be implemented. The /CS signal that activates the ADC0804 is developed from the eight high-order address lines of the MPU address bus. Whenever the MPU wants to communicate with the ADC0804, it places the address of the ADC0804 onto the address bus , and the decoding logic drives the CS signal LOW. Notice that in addition to the address lines, a timing and control signal (ALE) is connected to the E2 enable input. Whenever ALE is HIGH, it means that the address is potentially in transition, so the decoder should be disabled until ALE goes LOW (at which time the address will be valid and stable). This serves a purpose for timing but has no effect on the address of the ADC.
a) Determine the address of the ADC0804.
b) Modify the diagram of the figure to place the ADC0804 at address F9XX hex.
c)Modify the diagram of the figure to place the ADC0804 at address FAXX hex.

Solution

A)ADC0804 is an 8 bit successive approximation analogue to digital converter from National semiconductors. The features of ADC0804 are differential analogue voltage inputs, 0-5V input voltage range, no zero adjustment, built in clock generator, reference voltage can be externally adjusted to convert smaller analogue voltage span to 8 bit resolution etc. The pin out diagram of ADC0804